It is known that a public/private key infrastructure is (PKI) is an excellent mechanism to ensure that data remains confidential and unchanged during transit over insecure networks such as the Internet. The PKI is based on the premise that a user has two mathematically related numerical keys, a private key and a public key, which serve to encrypt data. It is possible to secure a message by encrypting it with a sender's private key and a receiver's public key, which is obtained from a repository known as a certificate authority (CA). The receiver can read the message by decrypting it using his private key and the sender's public key.
The keys used in the PKI are very long; and, the longer they are, the more secure the system is. It is not feasible, however, for a user to remember or input a long key, e.g., 64 character or longer, when the user wants to send or receive a message. To prevent unauthorized users from accessing private keys and thus falsely originating, reading or changing messages, private keys are usually protected by a secret code.
Secret codes such as a personal identification number (PIN) and a password can be compromised through the use of various techniques well known in the art. For instance, people often choose easy to remember pins and passwords, which also make them easy to guess. Birthdays, children's names and social security numbers are among the most commonly chosen. To combat this, many organizations require that passwords be changed often, and many PINs are assigned to is prevent easily guessed PINs. Unfortunately, many times this leads to people writing down the secret information, making it accessible to fraud perpetrators.
Shoulder surfing is also a known technique that can be used to compromise secret codes. This simply involves a fraud perpetrator watching over the shoulder of the person entering the code as a secret code is entered.
Also brute force attacks can compromise secret codes. This method simply involves rapidly entering many codes, until the secret one is stumbled upon. Long codes, mixing letters and numbers and frequent changing of codes can prevent the success of brute force attempts. Additionally, systems locking up after a predefined number of incorrect password attempts can prevent the success of brute force attacks.
If the private key is compromised by one of the various techniques, then it is no longer possible to ensure that information is kept confidential and unchanged. Therefore, the reliability of the PKI depends on any method used to secure the private key.
Various techniques have been suggested to enhance the performance of the PKI, such as securing the private key with biometrics instead of secret codes. Biometrics are more secure than secret codes; and therefore the security of the PKI can be enhanced. Biometrics are technologies that verify identity based upon one's physiological or behavioral characteristics, such as one's fingerprint, eye scan, voice print, hand geometry, facial image or signature. Biometrics can verify one's identity by either performing a one-to-one comparison to authenticate a submission or by performing a one-to-many comparison to identify one's submission out of a database containing a plurality of biometrics samples. A biometric sample is either the direct information obtained from the user, e.g., fingerprint, hand image, voice print, facial image, handwriting sample or facial image, or processed form of such information. For example, a biometric sample includes one's fingerprint and a minutia template based on one's fingerprint. By securing the private key with a biometric, the sender can assure the integrity of the private key so that a message using it will not be fraudulently originated. Likewise, a receiver protecting his private key with a biometric can rest assured that no one will be able to read the message that is intended for his eyes only. Only after a local verification of the biometric submission releases a local private key, the message can be originated or read.
However, even with a biometrically protected private key, neither party is assured that biometric authentication is processed on the other end. That is, the sender is not assured that the intended receiver is reading the message and the receiver is not assured that the intended sender sent the message. For example, neither party is assured that the other party uses a biometric, instead of a secrete code to protect the private key. There are myriad problems with one party relying on the other to use a biometric system to secure the private key. Neither party can be certain that other party has installed a biometric system on its computer; nor can they be certain that the other party's private key is securely protected by the biometric.
Furthermore, there is no quality control over enrollment. That is, there is no way to ensure that samples submitted during enrollment belong to a claimed enrollee. And a fake sample could have been enrolled. Additionally, neither party has any control over the environment of other party's computer. In other words, there could be a network of supercomputers working to hack into the biometrically protected key. Dozens of attempts might be made before a sample is falsely verified.
If the sender and the receiver know with certainty that the other's private keys are being secured with a biometric, and if they could receive, interpret and rely on a biometric verification score, then the process would be secure. In addition, there are different disciplines of biometrics (e.g., voice verification, finger scanning, iris scanning, retina scanning, hand geometry), and many vendors within each of these disciplines, each having its own accuracy levels. There is currently no infrastructure for interpreting the verification score of each of these vendors. As such, if the receiver learns that the sender is verified on a biometric system from a vendor with a score of 75, they would have difficulty in determining if this was a good match. Finally, there is no way for a sender or receiver to ensure that the results of a biometric comparison are in fact legitimate. Because in the conventional approach all biometric verifications are performed on local machines, there is no assurance that the biometric verification is processed as it should.
A revocation list used in the PKI is a list of certificates that have been compromised and are thus no longer valid. The fundamental problem with relying solely on this list to confirm that a certificate is being used by a legitimate user is that revocation lists are not immediately updated. The moment a private key is compromised it does not appear on the revocation list. No one, with the exception of the fraud perpetrator, knows that a compromise has taken place and certainly he or she will not notify the CA to add that certificate to the revocation list. In addition, once is the certificate is reported as compromised, there is a time lag before the distributed lists are updated. The real value of a revocation list is to prevent repeated fraud to be perpetrated on the same certificate.
Without the CBA infrastructure, individual institutions will have to maintain local databases of biometric enrollments. There are a number of problems with this scenario. First, there is a large overhead for a typical company to create and maintain a biometric enrollment for each customer. This includes the cost and time to properly identify each enrollee, train each enrollee on proper system use, etc. Second, customers may trust a company enough to buy from them, but may not want to enroll in their biometric system. Third, there are a number of bills pending relating to the use of such local databases. Companies risk losing the right to use their database in the manner they intend, or having a databases or related processes that do not comply with new laws. There could be substantial overhead in restructuring databases to comply with new laws. There are liability issues with maintaining databases of enrollments. It is preferable for companies avoid such risks and not maintain an internal biometric database.